1. Field of the Invention
The present invention relates to a circuit structure with organic thin film transistors; and more particularly to a circuit structure with a double-gate organic thin film transistor device.
2. Description of the Related Art
Because there is no any doping process involved in the manufacture of the current organic thin film transistor, the threshold voltage of the transistor device can not be controlled. The threshold voltage of the transistor device always relies on surface conditions of the device, the purity of the organic semiconductor material, and the material characteristics of the gate and gate insulating layers. The threshold voltage Vth is always too large up to ten volts or more, which makes not only power consumption but also loss of a certain voltage, and causing distortion of signal transmission in an application of electronic circuit. FIG. 1A and FIG. 1B are schematic circuit structures of two kinds of conventional inverters. The conventional inverter of FIG. 1A includes a first enhanced-type N channel transistor 10 and a second enhanced-type N channel transistor 12. The second enhanced-type N channel transistor 12 is an organic thin film transistor. Because the inverter has the second enhanced-type N channel transistor 12, there is a voltage difference of Vth between the output 14 of the inverter and the drain 16 of the second enhanced-type transistor 12, and resulting in the shift of an output signal value of the output 14. The transmitted signal is distorted. Due to the large threshold voltage of the organic thin film transistor, the signal distortion is more severe. For reducing the threshold voltage and improving accuracy of signal transmission, the inverter design of FIG. 1B is mostly adopted. This kind of the inverter includes an enhanced-type N channel transistor 10a and a depletion-type N channel transistor 12a. The depletion-type N channel transistor 12a is an organic thin film transistor. By surface treatment of the interface between the metal gate and N channel area, the depletion-type N channel transistor 12a is realized. During the current LCD display panel manufacturing process, the thin film transistor devices of the driving circuit area and the thin film transistor devices of the pixel area are simultaneously produced. When adopting the inverter design of FIG. 1B in the driving circuit of the LCD (Liquid Crystal Display) display panel and proceeding the surface treatment of the interfaces between the metal gates and N channel areas of the organic thin film transistors of the driving circuit area to make the organic thin film transistors become depletion type, the thin film transistors of the pixel area would also become depletion type. As a consequence, the switch elements of the pixel area will make mal-operation.
Accordingly, it is desirable to provide an improved circuit structure with the organic thin film transistor to alleviate the distortion of the signal transmission of the electronic circuit due to the too high threshold voltage of the organic thin film transistor.